THE INFUSORIA 



369 



Their particular arrangement on the surface of the body is one 

 of the chief characters used in classification, and will be described 

 under the several orders and sub-orders, but it may be mentioned 

 here that when the cilia are arranged in definite rows or circles 

 they are not infrequently united at their bases by a very delicate 

 membrane or webbing which may be called a membranella. 



In the remarkable parasites allied to TrichonympJia (Fig. 11), 

 some of the cilia appear to be of re- 

 markable length, and unlike ordinary 

 cilia in other respects. According to 

 Porter, the shorter cilia of the middle 

 region of the body are mainly re- 

 sponsible for the active movements so 

 characteristic of the parasite ; the 

 longer cilia, which cover the greater 

 part of the posterior region of the 

 body, vibrate but little, while the cilia 

 at the posterior extremity are abso- 

 lutely motionless. The function of 

 the motionless cilia appears to be to 

 entangle and hold particles of food 

 which are subsequently ingested by 

 the cortex of the body in this region. 



In another parasite, Pyrsonympha 

 vertens (Fig. 84), the body is covered 

 with a few short cilia, but an enor- 

 mously elongated and very delicate a, the nucleus ; b, granules of food. 



H j ,1 j ,v Parasitic in the intestine of white ants. 



process, called the peduncle, at the x eoo. 

 anterior end, penetrates deeply into 



the epithelium of the host's intestine and fixes the parasite 

 in its position. The nature of this peduncle is difficult to deter- 

 mine, but it is probable that it represents an extremely specialised 

 form of cilium adapted to the function it performs. This peduncle 

 may be as much as 75 p. in length and 1'5 //, in diameter. A 

 similar peduncle occurs in the Holotrichous parasite Blepharocorys 

 (Fig. 4). 



The cirri are very characteristic of the group Hypotricha, 

 although occasionally found elsewhere. They usually arise from a 

 broad base and rapidly narrow distally to an extremely fine point. 

 In section they may be round, oval, semicircular, or even polygonal. 

 The cirri found on the margin of Euplotes are regularly frayed out 

 at the ends, and the posterior cirri of the Oxytrichinae are very 

 much flattened (Fig. 1). In many of the larger forms of cirri it 

 can be shown that a bundle of very delicate lines or fibrils runs 

 from the base to the apex. The nature of these cirri has been 

 a subject of some discussion among microscopists, but the view 



24 



Fio. 11. 



TrichonympJia agilis, Leidy. The 



